High-performance size-exclusion chromatography of humic substances on the hydroxyethyl methacrylate column

Nanoparticles as vectors for antibiotic resistance: The association of silica nanoparticles with environmentally relevant extracellular antibiotic resistance genes

A relevant but yet unconsidered subset of particles that may alter the fate of extracellular antibiotic resistance genes (eARGs) are nano-scale particles (NPs), which are ubiquitous in natural environments and have unique properties. In this study, sorption isotherms were developed describing the association of linear DNA fragments isolated from widespread eARGs (blaI and nptII) with either micon-sized kaolinite or silica nanoparticles (SNPs), to determine if sorption capacity was enhanced at the nanoscale. For each isotherm, eARG fragments were added at five starting concentrations (5-40 μg/mL) to mixed batch systems with 0.25 g of particles and nuclease-free water. Sorption was quantified by the removal of DNA from solution, as detected by a Qubit fluorimeter. Isotherms were developed for eARGs of various fragment lengths (508, 680 and 861 bp), guanine-cytosine (GC) contents (34%, 47% and 54%) and both double and single stranded eARGs, to assess the impact of DNA properties on particle association. Sorption isotherms were also developed in systems with added humic acid and/or CaCl₂, to assess the impact of these environmental parameters on sorption. FTIR analysis was performed to analyze the conformation of sorbed eARGs. Desorption of eARGs was studied by quantifying the removal of eDNA from washed and vortexed post-sorption particles. Statistically significant irreversible sorption of eARGs to environmentally relevant NPs (humic acid functionalized silica nanoparticles) was demonstrated for the first time. Nano-emergent properties did not increase sorption capacity of eARGs, but led to a unique compressed conformation of sorbed eARGs. The addition of humic acid, increased CaCl₂ concentration and small DNA fragment size favored sorption. NPs showed a slight preference for the sorption of single-stranded DNA over double-stranded DNA. These findings suggest that NP association with eARGs may be a significant and unique environmental phenomenon that could influence the spread of antibiotic resistance.

Two-Dimensional Offline Chromatographic Fractionation for the Characterization of Humic-Like Substances in Atmospheric Aerosol Particles

Organic carbon in atmospheric particles comprises a large fraction of chromatographically unresolved compounds, often referred to as humic-like substances (HULIS), which influence particle properties and impact climate, human health, and ecosystems. To better understand its composition, a two-dimensional (2D) offline method combining size-exclusion (SEC) and reversed-phase liquid chromatography (RP-HPLC) using a new spiked gradient profile is presented. It separates HULIS into 55 fractions of different size and polarity, with estimated ranges of molecular weight and octanol/water partitioning coefficient (log P) from 160-900 g/mol and 0.2-3.3, respectively. The distribution of HULIS within the 2D size versus polarity space is illustrated with heat maps of ultraviolet absorption at 254 nm. It is found to strongly differ in a small example set of samples from a background site near Leipzig, Germany. In winter, the most intense signals were obtained for the largest molecules (>520 g/mol) with low polarity (log P ∼ 1.9), whereas in summer, smaller (225-330 g/mol) and more polar (log P ∼ 0.55) molecules dominate. The method reveals such differences in HULIS composition in a more detailed manner than previously possible and can therefore help to better elucidate the sources of HULIS in different seasons or at different sites. Analyzing Suwannee river fulvic acid as a common HULIS surrogate shows a similar polarity range, but the sizes are clearly larger than those of atmospheric HULIS.

Effect of Tris-HCl buffer on DNA adsorption by a variety of soil constituents

We investigated the effect of tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) buffer (pH 7.0) as a bulk solution on the adsorption of DNA by gibbsite, goethite, montmorillonite, kaolinite, synthetic and natural allophanes, two humic acids and two andosols. The natural allophane, gibbsite, kaolinite and an andosol adsorbed significantly more DNA in a 0.1 M Tris-HCl buffer than in a 0.1 M NaCl solution (t-test, P<0.005). In contrast, montmorillonite adsorbed significantly less DNA in the Tris-HCl than NaCl solution (P<0.05). Care should be taken when using Tris-HCl in studies on the adsorption of extracellular DNA molecules by soil particles.

Some theoretical and practical aspects in the separation of humic substances by combined liquid chromatography methods

Permanent need to understand nature, structure and properties of humic substances influences also separation methods that are in a wide scope used for fractionation, characterization and analysis of humic substances (HS). At the first glance techniques based on size-exclusion phenomena are the most useful and utilized for relating elution data to the molecular mass distribution of HS, however, with some limitations and exceptions, respectively, in the structural investigation of HS. The second most abundant separation mechanism is reversed-phase based on weak hydrophobic interactions beneficially combined with the step gradients inducing distinct features in rather featureless analytical signal of HS. Relatively great effort is invested to the developments of immobilized-metal affinity chromatography mimicking chelate-forming properties of HS as ligands in the environment. Surprisingly, relatively less attention is given to the ion-ion interactions based ion-exchange chromatography of HS. Chromatographic separation methods play also an important role in the examination of interactions of HS with pesticides. They allow us to determine binding constants and the other data necessary to predict the mobility of chemical pollutants in the environment. HS is frequently adversely acting in analytical procedures as interfering substance, so more detailed information is desired on manifestation of its numerous properties in analytical procedures. The article topic is covered by the review emphasizing advances in the field done in the period of last 10 years from 2000 till 2010.